The present invention relates to a smart keyless entry system, and more specifically relates to a smart keyless entry system in which a transmitter of an onboard device is disposed at a specified position which is off the center line of a vehicle compartment in a vehicle width direction.
The smart keyless entry system of the vehicle has been widely used in these days. A portable device of the smart keyless entry system performs the role of a conventional mechanical key. For example, when a card-shaped portable device is carried in a pocket or a bag, a door lock/unlock, an engine start and the like can be operated without using the key. In order to perform such a function, the vehicle is equipped with an onboard device operative to transmit a request signal in response to operations of access switches provided at outer faces of doors. The portable device transmits a receipt-acknowledge signal, such as an ID signal, in response to the request signal from the onboard device. When the ID signal from the portable device is verified (recognized), the onboard device activates onboard control devices to operate their functions, such as a door lock mechanism operative to unlock the door.
Japanese Patent Laid-Open Publication No. 2006-104664 discloses an example of such a smart keyless entry system in which the LF transmitting antennas are disposed at some points in the vehicle compartment.
In general, the output range of the signal from the transmitting antenna, which has sufficient signal strength, of the smart keyless entry system is of a circular shape with its center at the transmitting antenna. Therefore, it may be preferable that the transmitting antenna operative to transmit the request signal to the portable device be disposed on the center line of the vehicle compartment in the vehicle width direction.
However, on or around the center line of a front portion of the vehicle compartment in the vehicle width direction are provided various components, such as a console and a parking brake. Accordingly, it may be difficult to dispose the transmitting antenna of the onboard device of the smart keyless entry system at the central portion of the front portion of the vehicle compartment in the vehicle width direction.
Herein, in a case in which the transmitting antenna is disposed at a specified portion which is off this center line of the vehicle compartment, the respective distances from the transmitting antenna to the both-side doors of the vehicle would be different from each other. As a result, the signal strength of the respective request signals at the both-side doors become different from each other.
Therefore, if the output strength of the transmitting antenna is set in such a manner that its output range reaches one of the doors which is closer to the transmitting antenna than the other door, without reaching the other door, for example, the area of the other door is out of the output range of the request signal, so that there is a concern that it may be recognized (determined) by mistake that the portable device is located outside the vehicle compartment despite the inside existence of the portable device in the vehicle compartment. This may cause a problem in that the door is locked, leaving the portable device inside the vehicle compartment.
In the meantime, if the output strength of the transmitting antenna is set in such a manner that its output range can also reach the other door which is located further from the transmitting antenna, the closer door is included within the output range of the request signal. As a result, the portable device may be mistakenly recognized to be located inside the vehicle compartment despite its location outside the vehicle compartment. In this case, there may occur a situation in which the door unlock is not conducted even if the access switch at the door is operated.